In recent years, because of growing concern with environmental problems, demand to automobiles for fuel saving has increased and rubber compositions to be used for tires are also required to be superior in fuel saving efficiency. As rubber compositions for treads of tires, there have been used rubber compositions in which reinforcing agents such as silica are blended into diene-based rubbers such as polybutadiene and styrene-butadiene copolymers.
When silica is blended as a reinforcing agent into a diene-based rubber, a silane coupling agent is further blended in order to improve an affinity of the diene-based rubber and the silica, thereby improving the dispersibility of the silica. As a method for producing a rubber composition comprising a diene-based rubber, a silica reinforcing agent, and a silane coupling agent, a method for producing a rubber composition has been proposed, as disclosed in patent document 1, in which a diene-based rubber and a silica reinforcing agent are kneaded to prepare a pre-kneaded composition and then the pre-kneaded composition and a silane coupling agent are kneaded.